Catalytic cracking is accomplished by contacting hydrocarbons in a reaction zone with a catalyst composed of finely divided particulate material. The reaction in catalytic cracking, as opposed to hydrocracking, is carried out in the absence of added hydrogen or the consumption of hydrogen. As the cracking reaction proceeds, substantial amounts of coke are deposited on the catalyst. The catalyst is regenerated at high temperatures by burning coke from the catalyst in a regeneration zone. Coke-containing catalyst, referred to herein as “spent catalyst”, may be continually transported from the reaction zone to the regeneration zone to be regenerated and replaced by essentially coke-free regenerated catalyst from the regeneration zone. Fluidization of the catalyst particles by various gaseous streams allows the transport of catalyst between the reaction zone and regeneration zone.
One such regeneration zone is disclosed in U.S. Pat. No. 7,906,077, the entirety of which is incorporated herein by reference. The regeneration zone typically comprises a regenerator vessel that includes an outer shell and an internal riser. The internal riser is typically attached to the outer shell. However, given the extreme high temperatures that occur inside of the regenerator vessel, the riser will expand. Therefore, there is typically an annulus or void between the outer shell and the internal riser. In order to avoid catalyst from filing this void, one or more seals are used to keep the annulus relatively free from catalyst.
One known sealing system is shown in U.S. Pat. No. 5,328,667 in which a primary seal is disposed between the outer shell and the internal riser. A cone-shaped metal ring is disposed on the internal riser above the primary seal and contacts with a metal plate on the shell. The cone-shaped metal ring is welded to the riser and comprises a single piece. While these designs may be effective, it is believed that such a configuration may have some drawbacks.
For example, it has been observed that the weld between the riser and the ring has a tendency to crack as a result of the extreme temperatures in the internal riser and the weight of catalyst on top of the ring. Additionally, the design of the cone-shaped ring does not easily allow for inspection of the primary seal. Similarly, the design of the cone-shaped ring does not allow for easy removal of any catalyst that has accumulated under ring.
Therefore, there remains a need for an effective and efficient design for sealing an annulus between an internal riser and an outer shell in an FCC regenerator.